Importance of Bull × Herd-Year-Season Interaction in Milk Production

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Abstract
The bull x herd-year-season interaction was estimated from 129 balanced 2 by n groups of 2 sires by n herd-year-seasons using 305-day, 2x, ME milk production records. This interaction component of 313 kg2 was 2.0% of the total variance among individuals. Since the 95% confidence interval included zero, it is not established with statistical significance that the interaction was real. Consideration of different situations suggests that such an interaction would not cause appreciable errors in sire selection, except in special situations which are unlikely to occur when sires are progeny-tested in artificial insemination.